1. Technical Field
The invention relates to a device for administering an injectable product.
2. Description of the Related Art
Injection devices, for example injection syringes or injection pens, such as the invention relates to in particular though not exclusively, conventionally comprise a casing which accommodates an ampoule with the product to be injected, a delivering means for delivering the product out of the ampoule and a coupling means. The delivering means is conventionally formed by a piston which is movable in the ampoule. In simple syringes, the muscular power of the user serves as the drive means. The use of spring elements, in particular pressure springs, as the drive means is also known. The coupling means forms a transmission link or drive connection from the drive means to the delivering means.
The known drive means, for example drive springs, have the disadvantage that the drive force or drive energy applied by them is subject to changes in the course of being released. In drive springs, the drive energy changes in accordance with the spring characteristic. The delivering rate of the delivering means follows such changes. Correspondingly, the delivery rate changes in the course of delivery in accordance with the changing drive energy.
It is an object of the invention to provide a device for administering an injectable product, with which the product is evenly delivered in the course of an injection or infusion.
The invention is based on a device for administering an injectable product which includes a casing, a container for the product accommodated by the casing, a delivering means, a drive means and a transmission link or coupling means. The product is delivered directly out of the container by the delivering means. The drive means supplies the drive energy required for this, said drive energy being transmitted in the transmission link to the delivering means, in such a way that the delivering means is driven by the drive means, to deliver the product.
The container, the delivering means, the drive means and the transmission members of the transmission link are preferably arranged in the casing. Other arrangements are, however, in principle equally possible. The injectable product is preferably a medical or cosmetic agent, in particular in the form of a liquid active solution. A prominent example is insulin, administered using the device within the context of a treatment for diabetes. The device is preferably an infusion device. It can, however, also be an injection device. The container can, in particular, be formed as an ampoule, as is the case in known infusion devices. The delivering means is preferably formed by a piston accommodated by the container, which is advanced towards an outlet of the container, to deliver the product. However, instead of such a piston, the delivering means can in principle be formed by any type of pump suitable for delivering the product.
According to its type, the drive means is preferably formed in such a way that it releases the energy stored in it when it is triggered. Via a coupling means, this released energy is transmitted in the transmission link to the delivering means which, driven for its part in this way, delivers the product out of the container. The drive means is preferably formed by a drive spring, particularly preferably a pressure spring. In principle, however, other designs of drive means may also be used, e.g. those which release a pressure gas when triggered.
According to the invention, a fluid space for an incompressible fluid and a pressure reducing means are provided in the transmission link from the drive means to the delivering means, i.e. in the coupling means.
The fluid space correspondingly comprises a drive side, upon which the drive means acts, and a driven side, which acts on the delivering means. Both the drive side and the driven side can be connected, directly or via other transmission members, to the drive means and/or delivering means respectively. The fluid space can be impinged on its drive side by pressure from the drive means. The pressure thus generated is reduced toward the driven side of the fluid space by the pressure reducing means. The pressure is preferably reduced to a fifth or less and particularly preferably to a tenth or less by means of the pressure reducing means. The pressure reducing means creates a fluid connection which only allows a delayed flow of the fluid from the drive side towards the driven side, such that in a dynamic state, i.e. while the delivering means is being driven, a greater fluid pressure prevails on the drive side than on the driven side.
The invention enables a drive means to be used in which substantially more energy is stored than would be required to drive the delivering means and the resulting delivery of the product. The comparatively large drive energy released when the drive means is triggered is attenuated by the fluid coupling in accordance with the invention onto the measure required for delivering and administering. The excess of drive energy is available, controlled due to the fluid coupling in accordance with the invention, for driving the delivering means. If a drive spring is used as the drive means, as is preferred, then the spring strength of this drive means can be significantly higher than in the case of a direct drive connection to the delivering means. In particular, such a drive spring can be operated in a smaller range of its spring characteristic than would be possible in the case of a direct coupling.
Particularly preferably, a working stroke of the drive means is transmitted into a working stroke of the delivering means by the fluid coupling, said working stroke of the delivering means being greater than the working stroke of the drive means. In the case of a pressure or tension spring as the drive means and a piston as the delivering means, the respective working stroke is the stretching or straining of the spring and the distance covered by the piston in dependence on this working stroke. Particularly preferably, the delivering means is formed as a piston and the drive means likewise acts on a piston, designated in the following as a drive piston. In this embodiment, the drive side of the fluid space is formed by a piston area of the drive piston. The piston area of the drive piston is preferably larger than a piston area of a driven piston, wherein the piston area of the driven piston forms the driven side of the fluid space.
Through this ratio of the two piston areas, a stroke of the drive piston is transmitted into a comparatively larger stroke of the driven piston. Expressed differently, a smaller stroke of the drive piston is required to achieve a given stroke of the driven piston. The working stroke of the drive piston can be kept correspondingly short. The drive means can be operated in a tight range around its optimal operating point. Furthermore, the different-sized piston areas lead to a reduction of force. The force exerted by the drive piston is reduced in accordance with the ratio of the areas of the drive piston and driven piston. This reduction occurs in addition to the reduction of force as a result of the reduction of pressure. The Applicant reserves the right to independently further prosecute the feature of the different-sized piston areas, together with features a) to e) of claim 1.
The driven piston can form the delivering means directly. The driven piston is, however, preferably another piston.
In a particularly preferred example embodiment, the fluid space is sub-divided into a first partial space including the drive side and a second partial space including the driven side, and the two partial spaces are connected to each other exclusively by a system of capillaries, if a higher pressure prevails on the drive side than on the driven side of the fluid space. The system of capillaries can be formed by a single capillary or also by a plurality of capillaries.
The capillary or plurality of capillaries is/are advantageously as long as possible. Its/their length is preferably at least 0.5 m. If a plurality of capillaries are formed, this preferably applies to each of the capillaries. The through-flow rate in long capillaries is less dependent on the diameter of the capillary, as directly follows from the Hagen-Poiseuille Law. According to the Hagen-Poiseuille Law, variations in the diameter due to imprecision in production enter into the through-flow rate in the fourth power. However, with an increasing length of the capillary, its diameter can likewise be enlarged, if the through-flow rate is to remain constant. Larger diameters are on the one hand by their very nature simpler to produce than smaller diameters, and with an increasing size of the diameter, deviations from the desired diameter arise to an increasingly less important extent only. Furthermore, an as high viscosity of the working fluid as possible in the fluid space is preferred.
The system of capillaries preferably comprises a capillary running spirally, or a plurality of such capillaries. In a preferred example embodiment, the system of capillaries is formed by a single, spiral capillary. A spiral capillary not only has the advantage of a large length, but can also be simply produced. In particular, it can be formed in the form of an external or internal thread on a corresponding surface area, preferably a shell or jacket surface area, of a capillary body. The capillary body with the external or internal thread is preferably placed into or onto another body with a smooth opposite surface area, wherein care must be taken that the threads of the capillary body are sealed against each other on the opposite surface area.